Natural killer (NK) cells are defined as lymphocytes which lyse certain transformed or virally infected targets without prior sensitization or restriction for products of the major histocompatibility complex (MHC) (Herberman et al, Bolhuis et al, Trinchieri et al, Reynolds et al). Although T cells (CD3+) have been described with NK-like activity, classical NK cells are large granular lymphocytes which lack CD3 and express CD16 and/or Leu 19 (Lanier et al; Perussia et al, 1983; Hercend et al, 1985, 1988). Despite the fact that NK cells have a limited target cell range, no specific NK associated surface receptor or target ligand has yet been defined, leading to speculation that such effector cells lack a highly refined antigen recognition system. However, work done in support of the instant invention suggests that some NK cells lyse their targets with a high degree of specificity. Lymphocytes of NK phenotype (CD3-, CD16+) were cultured for several weeks with allogeneic microvascular endothelial cells (EC) or lymphoblastoid cell lines (LCLs) in the presence of medium containing growth factors such as IL2. The resulting NK cell lines, which retained their NK phenotype, displayed selective cytolytic activity against their specific stimulator line.